for the temperature, there are plenty of options, google thermistor.
some of the most simple are voltage-varying, whereby they output a different voltage dependent on their temperature.
whatever you end up doing, you will need a battery and a controller (chip) either within the helmet, or maybe hidden within some body padding with a small wire running up your neck?
i think you will have to do some programming regardless to get the system working, so some sort of development board will be needed. once its programmed though you can remove the chip to put it in a smaller package